Quote:

*Originally posted by wesleysh *

**Basic dB formula This formula is assuming that all things are perfect.**

It is a LOGICAL “Guessimate” that is ALWAYS within 3 dB of actual!

That voltage is near 14 volts/plenty of battery/alternator

Using at least 1/0 Ot guage wire

Some kind of Line Driver is being used

1st things first

Start off with sensitivity of the “raw” driver

Then total power of the amplifer (peak AC volts measured with a volt meter)

2nd thing

Calculate the total efficiency of the woofers

Add each woofer as + 3, doubling of cone area equals double output

For example: Take a CC-D1200, connected to 2 SS-12 (a load of 1 ohm)

You’ve measured the Ac volts out into this speaker load as 42 volts,

which calculates to 1764 “peak” watts. A/C volts squared (times itself) divided by

the impedance equals power. So.....42 X 42 = 1764 divided by the impedance, which

is 1ohm in this instance, so its still is...1764!!! We now know the REAL power

(cause you measured it into a REAL load...............The Concept SS-12 woofer)

The Concept SS-12’s are 87 dB 1W/1M (typical of ALL small box woofers *

Lets do the dB Log:

1 woofer = 87 dB

2 woofers = 90 dB

4-woofers = 93 dB

4th thing

Add up the special “side deals” Like is the boxed sealed (no extra dB), hatchback or coupe? Etc.

Use the following to get “close to the REAL DEAL in SPL.

Transfer Function (sedan) = 12 dB

Transfer Function (hatchback with woofers aming towards the rear glass) = 16 dB

Sealed box = No extra dB

Vented box = 3 dB (UNLESS you have an odd order alignment)

Vented box = 6-9 dB (IF an odd order alignment - Big *** box )

BandPass Box = 6-10 dB (depending on how small the enclosure is)

Mic Placement = 6 dB for DB drag dash/window mic placement

125 dB

3rd thing

Do the “dB log” starting with the total subwoofer (s) efficiently (which is 93 in this instance)

93 dB = 1 watt

96 dB = 2 watt

99 dB = 4 watt

102 dB = 8 watt

105 dB = 16 watt

108 dB = 32 watt

111 dB = 64 watt

114 dB = 128 watt

117 dB = 256 watt

120 dB = 512 watt

123 dB = 1024 watt

126 dB = 2048 watt

Obviously we only

have 1764 watts

so we’ll “split the difference”

So.... this car will play

Now lets total it all up 125 db - basic “dB log”

+12 dB - standard cab car with a direct facing woofer box

137

But the woofer box is vented in something other than “optimum” or flat

+ 6 dB

143

+ 6 dB DB drag dash/window mic placement

+ 6 dB

149 dB (+/- 3dB)